The invention generally relates to vehicle brakes, and more specifically to an improved vehicle brake rotor, and a process for making same.
Vehicle brake rotors are known and typically include a friction ring or disc to which is fastened a hub used to connect the ring to a vehicle wheel. As is well known, friction rings have opposing friction surfaces for engagement by brake pads mounted in vehicle calipers such that each of two pads engage a corresponding surface of the friction ring under driver control to stop the vehicle. The friction ring of the vehicle brake rotor rotates about a central axis, coincident with the rotational axis of the wheel to which it is attached.
To reduce vehicle brake rotor weight, and improve the vehicle brake rotor's heat dissipation efficiency, brake rotors made of two materials have become both more popular and common, particularly among high-end vehicles. Friction rings are typically cast from a ferrous material, such as cast or grey iron. The friction rings are then machined in multiple operations to shape the rotor and form an inner mounting section and the friction surfaces. The friction surfaces of the rotor are also machined to a predetermined tolerance range.
The hub of a vehicle brake rotor is typically cast from metallic materials such as aluminum. A conventional hub further includes a centrally located bore, and a plurality of equally spaced fastener mounting holes formed circumferentially in a mounting surface around the bore. Hubs are connected to the disc body, usually with a plurality of fasteners such as rivets, or threaded fasteners, such as screws. By connecting the hub to the friction ring, fasteners keep the hub and friction ring together. As a result, fasteners aid in movement of the vehicle brake rotor.
To accurately assemble the brake rotors made of two materials, complicated equipment is needed. Due to the high level of skill needed to operate such complicated equipment, the costs of manufacturing the two material vehicle brake rotor with fasteners are high.
Another drawback of conventional bi-metallic brake rotors is that a hub made of lighter materials has a higher expansion rate than the friction ring made of cast iron. When the vehicle brake rotor undergoes high temperature conditions, expansion of the hub and the friction ring will occur. Such expansion will further occur when the vehicle brake rotor and friction rings engage. There is a concern that multi-component brake rotors will be subject to shorter operational life due to the different expansion and contraction properties of the materials used in production. Thus, there is a need for an improved technique for manufacturing vehicle brake rotors.